Ryanair shares fell as much as 4.9% after it posted a third quarter loss for the first time in five years and said Michael O'Leary will step back from the day-to-day running of the airline.
A board restructuring will see Mr O'Leary become group chief executive and be replaced within the next 12 months as the day-to-day boss of the main airline.
Peter Bellew, Ryanair's chief operations officer; and the airline's chief commerical officer David O'Brien are thought to be frontrunners to replace him as Ryanair moves to a group structure similar to that of Aer Lingus and British Airways-owner IAG.
Mr O'Leary has signed a new five-year contract, putting him in charge of capital allocation, cost reduction, aircraft orders and group acquisitions. Longstanding Ryanair chairman David Bonderman is also set to leave, with former Kerry Group boss Stan McCarthy replacing him next year.
Ryanair posted a net loss of €19.6m for the three months to the end of December. It blamed the year-on-year reverse from a net profit of €105.6m entirely on weaker-than-expected air fares.
Passenger numbers grew 8% to 33 million people in the quarter - and grew again by 11% in January - but average fares fell 6% to under €30. The airline sees no end to low fares while there remains over-capacity in the European aviation market.
Third quarter revenue rose 9% to €1.53bn and ancillary revenue - which strips out air fares - increased by 26%, but was offset by higher fuel, staff and passenger reimbursement costs.
Ryanair's share price has fallen by over 30% in the past 12 months and is expected to trade between €9 and €14.50 for the next 18 months. It eventually closed down by just under 2% yesterday, after partially paring back earlier losses.
"Its shares may underperform in the short-term as earnings trend down, Brexit uncertainty weighs and growing concerns about industry competition with the low cost leader now operating at a loss," said Darren McKinley, senior equity analyst at Cantor Fitzgerald.
Mr McKinley, however, said the change in management structure should help ease further strike action.
He also expects Ryanair to miss its €1bn-€1.1bn profit guidance for the 12 months to the end of March. He said profit levels of around €1.45bn per year - last seen in March 2018 - are unlikely to be seen until around 2022, and expects a net profit of between €875m and €975m for the current year.